Medical electrodes have been used for years to accomplish various clinical functions, including nerve stimulation, bio-feedback monitoring, electromyographs, and electroencephalograph (EEG) tests, to name a few. Medical electrodes are designed to either send electric current, from an electrical medical device to a living being, or else receive electric current generated by a living being. Medical electrodes can be used in both a human patient environment and in a veterinary environment.
Medical electrodes are generally comprised of a proximal end for coupling to a patient, a distal end for connecting to a medical appliance, such as an EEG machine, and an elongate wire lead located between the proximal and distal ends, for receiving or sending electrical current. Of these elements, the proximal end varies in structure according to the function necessary for a particular medical procedure. The different structural configurations of the proximal end of exemplary electrodes, include needle, plate, snap, and corkscrew electrodes, to name a few.
The passage of electrical current through a medical electrode is usually accomplished according to safe protocols, and generally does not result in any injury to a patient. However, it has been documented in a number of cases that the passage of current through a medical electrode connected to a patient has resulted in tissue burns, and even death by electrocution. The inventor has traced these unfortunate incidents back to five basic causes: 1) Equipment Failure; 2) Induction Current Phenomena; 3) Defective Machine and/or Defective Grounding of a Machine; 4) Constant DC current; and 5) Plugging an electrode having a male adaptor distal end directly into an AC power source.
The following actual case incidents, which are exemplary of each of the causes listed above, are being submitted here to further inform the reader of the problems with electrodes presently existing in the medical arts:
Case 1—Equipment Failure
An external stimulator hooked to a patient's ankle with medical electrodes was used with a computer averager to record somatosensory evoked potentials. The computer was wired so that it would drive the stimulator and record the averages of the potentials. During this case, an electro-cautery device was moved near a cord coupled to the external stimulator. The electro-cautery put out an inductive current that was strong enough to trigger the stimulator at a rate that was tied to the oscillating rate of the electro-cautery. This case lasted for eleven hours, at the end of which time, the stimulating platinum-iridium needle electrode tips were examined. It was found that enough heat had been generated such that the needles had vaporized and left a hole in the patient's ankle.
Case 2—Inductive Current Phenomena
A technician had encountered a minor problem with an electrode burn on a patient, which had occurred during feedback to an electro-cautery machine being used in an operating room, while performing a neuromonitoring procedure. The technician, being concerned about the possibility of this happening again, decided to disconnect the neuromonitoring equipment from the distal end of the electrodes, when she was not taking actual readings. However, the proximal ends of the electrodes remained connected to the patient. The technician coiled the disconnected electrode leads up, and taped them to a bed frame holding the patient, so that they would be out of the way, and available when she needed them again. A surgeon then used the electro-cautery equipment again, and this surgeon had a habit of pressing the “on” button of the electro-cautery probe when it was away from the patient. This particular electro-cautery probe used a very high voltage current and when the probe was turned on, away from the patient, the current took the path of least resistance into the coiled wires. The coiled wires acted as an induction coil receiver and further amplified the signal causing a significant bum on the patient.
Case 3—Defective Machine and/or Defective Grounding of a Machine
A neuromonitoring technician placed skin surface electrodes on a patient, but did not insure that the grounding impedances were low. The technician then recorded somatosensory evoked potentials for a back surgery. The electro-cautery being used in the surgery was faulty, and the neuromonitoring equipment allowed current to pass from the patient to the ground leads and caused bums upon the patient.
Case 4—Constant D.C. Current
An experienced engineer was testing equipment and placed a 1.5 volt D.C. battery in line with some equipment that he was testing on himself, while he had a pair of needle electrodes connected to his hand. The engineer became so focused on his work that he did not bother to remove the electrodes for over two hours. He did not notice that he was developing an electrolytic bum on this hand from the constant D.C. current, and now has a permanent scar.
Case 5—Plugging an Electrode Directly into an AC Power Source
In 1985, the first reported incidents of electrocution deaths from the exposed male connector pins of electrode lead wires being plugged into either AC power cords or wall outlets were recorded. Between 1985 and 1994, 24 infants or children received “macro-shock” (large externally applied currents) from medical electrodes, including five children who died by electrocution. These incidents were documented in the background section of the Apr. 28, 1997 final rule making for 21 CFR Part 898 entitled: “Medical Devices; Establishment of a Performance Standard for Electrode Lead Wires and Patient Cables” authored by the United States Food and Drug Administration (FDA).
The previous case examples demonstrate that medical electrode injuries and death can occur under a variety of real-world conditions. However, to date, the major focus with regard to medical electrode safety measures has been to deal with the electrocution problem, because this is the problem that can have the gravest consequences.
As noted in case 5, above, electrocution has resulted from the distal ends of medical electrodes, which have traditionally had male connector pins, being plugged into an AC power wall outlets. The solution, thus far, has been to change the distal end of medical electrodes to female connectors, thereby eliminating the male connector pins. Due to the fact that medical devices which couple to the electrodes still, by in large, require a male input, this problem has been solved by providing adaptors which couple a male pin back onto the female connector, which, in turn, is plugged into the medical device. These adaptors typically bear warning indicia such as “Warning: Do Not Use With AC Power Source or Apnea Monitors.” However, these adaptors still convert the female connector end back to a male end, which despite such warnings, still present a real possibility of causing electrocution from plugging into a wall outlet.
Moreover, while the addition of adaptors present a better solution to the problem of electrocution from wall sockets, adaptors do not solve the problem of tissue bums and electrocution due to induction current phenomena. Induction current phenomena can be caused by RF leakage from defective medical devices such as an electro-cautery, or else can be cause from perfectly good devices, such as an MRI, which, by their nature produce significant amounts of electromagnetic energy. As noted in case 2, above, this induction current phenomena can occur when the electrode leads are uncoupled from a medical device, or an AC power source. So far, the answer to this inductance problem has been to post warnings on electrode packaging of the type shown on the packaging produced by Astro-Med, Inc., Grass Instrument Division of West Warwick, R.I. While package warnings certainly help keep medical personnel alert to the inductance problem, mere warnings are insufficient to stop tissue all tissue burns and electrocutions from occurring.
Various means have been devised for electrical medical appliances, in general, to prevent the passage of harmful current causing injuries or death. U.S. Pat. No. 5,433,732 (Hirschberg et al.) discloses an implantable heart defibrillator comprising a charging circuit located inside a housing with exterior electrodes for providing defibrillating current to a patient's heart. A complex current limiter is provided, exterior to the charging circuit, and in-line with the electrode wires. The current limiter prevents heart-damaging current from passing through to the electrode terminus. U.S. Pat. No. 4,418,692 (Guay) discloses an electro-cautery tip, which has a circuit breaker inside of the tip, for reducing the possibility of accidental activation of the device, which could damage tissue. Finally, the following patents disclose various electrical medical devices that have a fused component located in the circuitry of the device: U.S. Pat. No. 4,520,818 (Mickiewicz), U.S. Pat. No. 4,548,207 (Reimels), U.S. Pat. No. 4,363,324 (Kusserow), U.S. Pat. No. 4,494,541 (Archibald), U.S. Pat. No. 4,303,073 (Archibald), U.S. Pat. No. 4,301,801 (Schneiderman), U.S. Pat. No. 4,898,169 (Norman et al.).
While current stoppage means such as circuit breakers, current limiters, and fuses have been applied in the medical arts with regard to electrical medical devices, solutions for medical electrodes remain wanting. Many of the case histories noted previously involved electrical devices that had some type of built-in current stoppage means, yet harmful current was still passed to the electrodes to injure patients. Therefore, past solutions, have been inadequate to prevent the problem of bums and electrocution from harmful current passage through electrodes. Also, to this day, the international standards for medical electrical equipment (International Electrical Commission publication 60601-2-401) issue clear warnings regarding the danger of bums existing at the site of medical electrode input. These standards clearly show that as of yet, medical electrode design has not provided any closure to this burning problem.
Therefore, a need exists for a medical electrode that can both prevent injuries and death due to electrocution, from AC power sources and also injuries due to the inductance current phenomena.
The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventors' acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.